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Open Source and information security mailing list archives
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Date: Fri, 4 Jul 2014 14:20:45 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Mike Galbraith <umgwanakikbuti@...il.com> Cc: Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, riel@...hat.com, mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, sbw@....edu Subject: Re: [PATCH RFC tip/core/rcu] Parallelize and economize NOCB kthread wakeups On Fri, Jul 04, 2014 at 08:01:34AM +0200, Mike Galbraith wrote: > On Thu, 2014-07-03 at 22:05 -0700, Paul E. McKenney wrote: > > On Fri, Jul 04, 2014 at 05:23:56AM +0200, Mike Galbraith wrote: > > > > Turn it on and don't worry about it is exactly what distros want the > > > obscure feature with very few users to be. Last time I did a drive-by, > > > my boxen said I should continue to worry about it ;-) > > > > Yep, which is the reason for the patch on the last email. > > > > Then again, exactly which feature and which reason for worry? > > NO_HZ_FULL. I tried ALL a while back, box instantly called me an idiot. > Maybe that has improved since, dunno. Ah, I was thinking in terms of RCU_CPU_NOCB. > Last drive-by I didn't do much overhead measurement, stuck mostly > functionality, and it still had rough edges that enterprise users may > not fully appreciate. Trying to let 60 of 64 cores do 100% compute > showed some cores having a hard time entering tickless at all, and > ~200us spikes that I think are due to tick losing skew.. told Frederic > I'd take a peek at that, but haven't had time yet. There were other > known things as well, like timers and workqueues for which there are > patches floating around. All in all, it was waving the men at work > sign, pointing at the "Say N" by the config option, and suggesting that > ignoring that would not be the cleverest of moves. Well, I am not going to join a debate on Kconfig default selection. ;-) I will say that two years ago, setting NO_HZ_FULL=y by default would have been insane. Perhaps soon it will be a no-brainer, and I am of course trying to bring that day closer. Right now it is of course a judgment call. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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